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Effect of weight on boat speed

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Post Options Post Options   Quote Sam.Spoons Quote  Post ReplyReply Direct Link To This Post Posted: 24 Oct 20 at 4:35pm
  LOL Yup.... 'precisely' 
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Post Options Post Options   Quote NickA Quote  Post ReplyReply Direct Link To This Post Posted: 28 Oct 20 at 10:06pm
There are two kinds of 3000 class dinghy hulls, one weighs about 79kg and the other about 55kg. The light version is faster, but mostly because is requires less wind to get planing. When it's windy enough for both to plane the weight doesn't matter so much and they're about the same speed. In very light wind the difference is also small .. I guess, because it's hull length rather than displacement that's speed limiting. In marginal planing conditions a lighter boat will be surprisingly faster... Otherwise not to much, though acceleration in gusts is better.
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Post Options Post Options   Quote Sam.Spoons Quote  Post ReplyReply Direct Link To This Post Posted: 28 Oct 20 at 11:01pm
Yes, that's my feeling too, sub-planing and waterline length is king, when everybody's planing hull form is the decider (and irrelevant in a strict one design as they are all the same shape) it's only in marginal planing where hull weight makes a significant difference*. Of course that is slightly frustrating for me sailing a boat who's whole raison d'Ítre is to plane early and fast, with an old and moderately overweight hull. Equally eating a few less pies (and drinking less beer, but that would be a step too far) could easily compensate for the 5kg difference...

* it was much the same when I was racing Raceboards except the benefits of early planing were magnified tenfold compared to dinghies, and the benefits of abstinence were similarly magnified on those marginal days...


Edited by Sam.Spoons - 28 Oct 20 at 11:04pm
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Post Options Post Options   Quote whitsundays Quote  Post ReplyReply Direct Link To This Post Posted: 05 Nov 20 at 9:40am
A boat sails since it displaces more water than it weighs. More weight consistently implies more inertia, so the heavy boat needs more capacity to get to a similar speed. On the off chance that you analyse two in any case comparable boats, the heavier one will sit lower in the water, making more frictional and wave obstruction also.
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Post Options Post Options   Quote Sam.Spoons Quote  Post ReplyReply Direct Link To This Post Posted: 05 Nov 20 at 1:42pm
Somebody said this elsewhere and it is incorrect, at least insomuch as a boat floats because it displaces exactly the same weight of water as it weighs (a boat's weight is often termed it's 'displacement').

Edited by Sam.Spoons - 05 Nov 20 at 1:43pm
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Post Options Post Options   Quote A2Z Quote  Post ReplyReply Direct Link To This Post Posted: 05 Nov 20 at 2:21pm
Yes indeed.  And, as mentioned before, that is not an explanation of *why* a boat floats.  It floats because there is hydrostatic pressure acting on the wetted surface area of the hull, and the resulting force is equal and opposite to the weight of the boat.  
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Post Options Post Options   Quote Sam.Spoons Quote  Post ReplyReply Direct Link To This Post Posted: 05 Nov 20 at 2:39pm
Perhaps I should have said "when a boat floats it displaces exactly the same weight of water as it weighs"?
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Post Options Post Options   Quote 423zero Quote  Post ReplyReply Direct Link To This Post Posted: 05 Nov 20 at 3:00pm
Plus it's less dense due to air space in Hull.
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Post Options Post Options   Quote Sam.Spoons Quote  Post ReplyReply Direct Link To This Post Posted: 05 Nov 20 at 5:58pm
Windsurfers float and most don't have air space inside  Big smile
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Post Options Post Options   Quote 423zero Quote  Post ReplyReply Direct Link To This Post Posted: 05 Nov 20 at 6:05pm
They are full of foam.
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